1. Field of the Invention
The present invention relates to, an apparatus for focusing a particle beam, and in particular to an apparatus for focusing a particle beam using a radiation pressure capable of controlling the width of a particle beam
2. Description of the Background Art
A particle beam represents that the flow of a particle has a beam type. In the case that particles flow in a beam type narrow region, the number concentration of particles is increased, so that it is possible to monitor particles with high accuracy. In addition, since the particles continuously flow in a beam type, it is possible to measure the sizes of particles and a particle size distribution in real time. Therefore, a particle beam focusing apparatus has been used for a mass analyzer or a chemical composition analyzer. Recently, it has been used in a micro particle monitoring apparatus in which particles rarely exist like in a semiconductor process.
In the conventional art, a particle beam focusing apparatus has been generally used as an apparatus for generating particle beams wherein an aerodynamic lens is used therein. In the particle beam focusing apparatus using an aerodynamic lens, a particle flows but of an airflow way using an inertia effect of particles while air-particle flow passes through an orifice. The above particle beam focusing apparatus has an advantage in that it is possible to easily generate particle beans.
FIG. 1 is a view illustrating a conventional particle beam apparatus using an aerodynamic lens, and FIG. 2 is a view illustrating an air-particle flow in an orifice part of FIG. 1. As shown in FIG. 1, in a particle beam focusing apparatus using an aerodynamic lens, there are provided a particle generator 7, an air-particle mixing tube 1, a flow tube 2 that is provided at one side of the mixing tube 1 for thereby guiding air-particle to flow along a straight line, and an orifice part 3 that is provided at a predetermined portion of the flow tube 2 wherein the orifice part 3 has a hole 31 with a certain diameter and is formed in a flat plate shape.
In addition, as shown in FIG. 2, the particles from the particle generator 7 are supplied to the mixing tube 1. The air-particle mixed with the air in the mixing tube 1 is discharged through the flow tube 2. The air-particle flow discharged from the mixing tube 1 passes through the orifice part 3, and the particles are collected at the center from the flow of the air by an inertia force, so that the air-particle flow is formed in a form of particle beam. A contraction factor η representing a particle beam formation performance has been generally used. Here, the contraction factor η may be expressed in such a manner that a ratio (η=γp(∞)/γo(∞)) of the radius (γp) direction position of an outer most particle trace with respect to the radius (γo) direction position of the air outer most streamline is expressed after the air-particle flow passes through the orifice part 3. In the case that the contraction factor is 0, it represents that particles are collected at the center axis, and in the case that the contraction factor is 1, it represents that the particles flow along the air flow way. In the case that the contraction factor is a negative number, it means that the particles cross the center axis. Therefore, in the case that the particle beam is formed, the contraction factor has a value of −1<η<1.
However, in the case that the particle beam apparatus using the aerodynamic lens is adapted, the width of the particle beam that can be obtained under the set flow condition and the size of available particles are limited. In addition, on the contrary, there are disadvantages that the width of the particle beam that can be obtained with respect to the set size of the particle and the available flow amount are limited. Namely, it is needed to change the design of the particle beam apparatus. As one example, a certain research has been conducted for decreasing the width of the particle beam using a multistage type aerodynamic lens having a plurality of orifices. In the case that the multistage type aerodynamic lens is used, the particle beam apparatus gets complicated, and the disadvantages in the operation particle size and the flow condition of the aerodynamic lens still remain.